I encountered an absolutely wonderful piece on Youtube being performed by a small group of zitherists. At the following link, the song begins ~ 4:50, but is also used as background music throughout the video. I can only guess that it's an early classical piece arranged for Z. Any ideas?

If you bring back that YouTube page and look at the comments, you will see that I asked there and (surprisingly!) got the answer:
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Volksmusikarchiv des Bezirks Oberbayern
Krankenhausweg 39
83052 Bruckmühl